The invention relates to a method of header detection and protection, and more particularly, to in an optical storage system using a protection range signal corresponding to the header to correctly determine a property of the header.
Although typical optical discs, such as compact discs (CDs) according to the related art, conveniently provide user data storage, the storage capacity is limited. More and more, this limited storage capacity is becoming insufficient and unable to meet users' needs. Because of this, the storage industry has developed some new optical disc standards having increased storage capacity when compared with the original compact disc. One example is the digital versatile disc (DVD) standard. The DVD standard includes several specifications including DVD-R, DVD-RAM, DVD-RW, etc. However, all the DVD standards have several characteristics in common, such as specifying the same physical size as typical CDs, yet have substantially increased storage capacity. When an optical storage system accesses a CD or a DVD, an optical pick-up is used to read data stored on the optical disc or to perform data writing operations to store data onto the optical disc. Furthermore, when accessing the optical disc, the pick-up head must be positioned at a target track before the read or write operation can take place. When the pick-up head is performing track seek operations or tracking operations, the optical disc position, speed, and direction are important parameters that must be controlled.
Similar to CDs, information recorded on DVDs is stored in a plurality of data tracks. Using the DVD-RAM specification as an example, data tracks are formed using a single spiral track structure. Please refer to FIG. 1. FIG. 1 shows a section of a data track 10 on a typical DVD-RAM optical disc and includes a first data track 101, a second data track 102, and a third data track 103. Data tracks on a DVD-RAM optical disc comprise two different types of carrier regions being aligned around the DVD optical disc: groove tracks Gr and land tracks Ld. Unlike CDs, information recorded on DVD-RAM optical discs is not simply recorded using the groove tracks Gr, but is also recorded using the land tracks Ld positioned between the groove tracks Gr to store information. Because data is at the same time stored to both the groove tracks Gr and the land tracks Ld, and because the gap distance between the two carrier regions is maintained, when compared to typical CDs, in which the data follows along and uses only the groove tracks Gr, the data density in a DVD disc is increased by a factor of two. As shown in FIG. 1, stored data is recorded in sectors in both the groove tracks Gr and the land tracks Ld in each data track 10. DVD-RAM optical discs allocate a Complementary Allocated Pit Address (CAPA) at the start of each sector, which is stored in a header Hd. Therefore, one header Hd is stored between the groove track Gr and the land track Ld for each loop of the spiraled track structure of the data track 10.
In an optical storage system, in order for the optical pick-up to read data stored on an optical disc such as a DVD-RAM optical disc, the optical pick-up emits a laser beam to form a focused light point on the optical disc. Reflected light is then received from the DVD-RAM optical disc by the optical pick-up. Please refer to FIG. 2. FIG. 2 shows the relative positions of two data tracks (the first data track 101 and the second data track 102) from FIG. 1 and an optical detector 13 of an optical pick-up 12. The arrow AR in FIG. 2 indicates the track direction of the DVD-RAM optical disc. The detector 13 of the pick-up 12 follows this track direction AR on the first data track 101 and the second data track 102 to form a read data signal for the DVD-RAM optical disc. The optical detector 13 is divided into four quadrant sensors: a first sensor A, a second sensor B, a third sensor C, and a fourth sensor D. The optical detector 13 receives a light beam reflected by pits on the optical disc and, according to the amount of reflected light that lands on each quadrant of the optical detector 13, produces a corresponding electrical signal. As mentioned above, because data stored on a DVD-RAM is stored in both the groove tracks Gr and the land tracks Ld, each data track 10 simultaneously includes both a groove track Gr and a land track Ld. However, when the optical pick-up is reading data, a decision must be made of whether to focus the light beam on the groove track Gr or the land track Ld, and a decision must be made to determine each switch-over point. Additionally, a typical optical storage system includes an object lens, which is used to focus the laser beam emitted by the optical pick-up 12 on the DVD-RAM optical disc. As shown in FIG. 3, when the optical pick-up 12 is performing tracking operations on the groove track Gr and the land track Ld, the polarity of a controlling signal (TRO) changes by 180 degrees. The controlling signal (TRO) changes the polarity according to the tracking error (TE) sensor gain 15, which changes the polarity of tracking error (TE) by the decision signal JS of groove/land track. Additionally, the controlling signal (TRO) is used to control a coil motor 14 that adjusts the object lens. As such, accurately deciding whether to follow the groove track Gr or the land track Ld is very important in order to accurately control the optical pickup 12 and the object lens adjustment operation. Because each loop of the spiral structure of the data track 10 only contains a single switch-over point, which represents a switch over from the groove track Gr to the land track Ld or from the land track Ld to the groove track Gr, the polarity of the coil motor 14 control signal (TRO) needs to change one time when the optical pick-up 12 accesses data during each turn of the DVD-RAM optical disc. Otherwise, the object lens will lock on the wrong track and cause data read errors.
As shown in FIG. 2, the header is divided into four sub-headers: a first sub-header Hd1, a second sub-header Hd2, a third sub-header Hd3, and a fourth sub-header Hd4. The first to the fourth sub-headers (Hd1-Hd4) of the header Hd are located according to a set alignment sequence for each track. Positioned at the switch-over point between the different carrier regions, ½ of the sub-headers are located to the left of a center line between the groove track Gr and the land track Ld, and ½ of the sub-headers are located to the right of the center line. This property of the first to the fourth sub-headers (Hd1-Hd4) not only indicates the physical position of the header Hd, but also allows the optical storage system determine whether to follow the groove track Gr or the land track Ld. The most direct method for determining which carrier region (track type) to follow involves using the relative positions of the four sub-headers at the switch-over point. Because the sub-headers have different positions, the four quadrant sensors of the optical detector 13 generate different detection signals. This header Hd property allows a decision to be made of whether the next sector uses the groove track Gr or the land track Ld. Please refer to FIG. 4. FIG. 4 shows a functional block diagram of an optical storage system 20 according to the related art. The optical storage system 20 includes the optical detector 13 of FIG. 2, an optical pickup module 22, a first comparator 24, a second comparator 26, and a decision device 28. When the optical pick-up 12 passes a header Hd, as shown in FIG. 2, the optical pickup module 22 uses the optical signals received by the four quadrant sensors (A, B, C, D) of the optical detector 13 to produce a push-pull signal PPS and an RF-sum signal RFS. In this implementation, the four quadrant sensors (A, B, C, D) of the optical detector 13 each produce a corresponding output signal (a, b, c, d). The value of the push-pull signal PPS is [(a+b)−(c+d)], and the value of the RF-sum signal is (a+b+c+d). Next, the first comparator 24 and the second comparator 26 use the push-pull signal PPS to generate a first detection signal DS1 and a second detection signal DS2. More specifically, the first comparator 24 compares the push-pull signal PPS to a positive comparator voltage to determine the high voltage pulses of the push-pull signal PPS that exceed the positive comparator voltage and thereby generates the first detection signal DS1. Using a similar method, the second comparator 26 compares the push-pull signal PPS to a negative comparison voltage and determines the low voltage pulses from the push-pull signal PPS that are lower than the negative comparator voltage and thereby generates the second detection signal DS2. Finally, according to the first detection signal DS1 and the second detection signal DS2, the decision device 28 decides the header type.
An example using both FIG. 2 and FIG. 4 is described as follows. When the optical pick-up 12 follows the land track Ld in the direction shown for the first data track 101 in FIG. 2 and the track type after the header Hd remains the land track Ld, the C quadrant sensor and the D quadrant sensor of the optical detector 13 first detect the first sub-header Hd1 and the second sub-header Hd2. The A quadrant sensor and the B quadrant sensor of the optical detector 13 then detect the third sub-header Hd3 and the fourth sub-header Hd4. The signals (c+d), corresponding to the first and second sub-headers Hd1, Hd2, lead the signals (a+b), which correspond to the third and fourth sub-headers Hd3, Hd4. Please note that when switching from the land track Ld to the groove track Gr, the A quadrant sensor and the B quadrant sensor of the optical detector 13 first detect the first sub-header Hd1 and the second sub-header Hd2. The C quadrant sensor and the B quadrant sensor of the optical detector 13 then detect the third sub-header Hd3 and the fourth sub-header Hd4. Because of this, in the ideal situation, the signals (a+b), corresponding to the first and the second sub-headers Hd1, Hd2, lead the signals (c+d), which correspond to the third and the fourth sub-headers Hd3, Hd4.
Please refer to FIG. 5. FIG. 5 shows a timeline diagram of the signals of FIG. 4 in the ideal operating environment and includes the push-pull signal (including a non-filtered push-pull signal NPPS and a filtered push-pull signal PPS), the first detection signal DS1, and the second detection signal DS2. FIG. 5 shows the signal changes as a focused light point ST moves along the first data track 101. As previously mentioned, according to the related art, the first comparator 24 and the second comparator 26 use the predefined positive and negative comparator voltages (shown in FIG. 5 as the dotted lines through the push pull signal PPS) to generate the first and the second detection signals DS1, DS2 having different phase/time relationships. The first detection signal DS1 corresponds to the signals (a+b) produced according to first and the second sub-headers Hd1, Hd2. The second detection signal DS2 corresponds to the signals (c+d) produced according to the third and the fourth sub-headers Hd3, Hd4. In this implementation example, when the optical pick-up 12 is following along a land track Ld, the second detection signal DS2 leads the first detection signal DS1. However, when the optical pick-up 12 needs to switch from a land track Ld to a groove track Gr, the first detection signal DS1 leads the second detection signal DS2. In this way, the change of the lead/lag relationship between the first detection signal DS1 and the second detection signal DS2 indicates that the system must switch between the land track Ld and the groove track Gr. The decision device 28 shown in FIG. 4 toggles the value of an output decision signal JS and the polarity of the controlling signal for the object lens coil motor. Using the same logic, if the optical pick-up 12 in FIG. 2 is following the groove track Gr of the second data track 102, the optical system 20 shown in FIG. 4 produces corresponding signals allowing an adjustment from the groove track Gr to the land track Ld. In other words, carrier region selection is performed in the same way.
However, in reality, the focused light point ST produced by the optical pickup 12 often does not accurately follow the data track (the first data track 101) but instead sometimes deviates from the track center. This induces a track slippage phenomenon during track seek operations and also causes instability when following a groove track Gr or a land track Ld. Due to these problems, errors appear in the decision signal JS and the polarity of the object lens coil motor polarity, and the object lens locks on the incorrect track.
Please refer to FIG. 6. FIG. 6 shows a timeline diagram of the signals of FIG. 4 and FIG. 5 in a more realistic operating environment and includes the push-pull signal (including the non-filtered push-pull signal NPPS and the filtered push pull signal PPS), the first detection signal DS1, the second detection signal DS2, and the decision signal JS. As shown in FIG. 6, the focused light point ST does not accurately follow the first data track 101. Because when passing the switch-over point from the land track Ld to the groove track Gr the focused light point ST has already deviated from the original data track 10 (for example because of the track slippage phenomenon), the header Hd detection is flawed and the push-pull signal PPS is unstable. As such, the original predefined (positive and negative) comparator voltages do not cause the first comparator 24 and the second comparator 26 to generate correct first and second detection signals DS1, DS2. This causes an incorrect value on the decision signal JS and results in an incorrect polarity change on the coil motor control signal and instability of the system as a whole.